1. Field of the Invention
The present invention generally relates to a clamping apparatus including a fixed die plate and a moving die plate opposed to each other in the horizontal direction to open and close a die by moving the moving die plate forward and backward along tie rods supported to the fixed die plate and, particularly, to a clamping apparatus in which a moving die plate can move forward and backward smoothly with reliability and in which clamping accuracy can be prevented from being deteriorated even when a load is applied to one side of the moving die plate.
2. Description of the Related Art
According to the related art, a clamping apparatus for use in a horizontal injection-molding machine comprises a fixed die plate fixed to a frame, a plurality of tie rods extending in the horizontal direction and respectively supported to the fixed die plate in parallel to each other, a moving die plate supported to a plurality of tie rods so as to slide freely and a clamping mechanism for moving the moving die plate forward and backward along a plurality of tie rods.
The fixed die plate is composed of a square block-like member, and two to four tie rods are mounted to a plurality of portions of the fixed die plate. In the case of a clamping apparatus using four tie rods, for example, respective ends of the four tie rods are fixed to four corners of the fixed die plate. The four tie rods are parallel to each other and extend in the horizontal direction such that they may extend through the moving die plate so as to slide freely. A drive mechanism of a suitable drive system such as a direct pressure system, or a toggle system comprising a hydraulic cylinder, is coupled to the moving die plate to move the moving die plate forward and backward. When this drive mechanism operates, the moving die plate moves back and forth along the four tie rods to open and close a pair of dies fixed to the fixed die plate and the moving die plate.
However, in the clamping apparatus according to the related art, two to four tie rods are inserted into bushes of the moving die plate, and the moving die plate is supported so as to slide freely in the horizontal direction by the engagement state among the tie rods and the bushes for supporting these tie rods. For this reason, because the outer peripheral surface of the tie rod and the inner peripheral surface of the bush cannot contact with each other highly uniformly without difficulty, it is difficult or impossible to move the moving die plate smoothly and parallelly.
Specifically, in the clamping apparatus including the guide structure to guide the moving die plate by the engagement among a plurality of bushes on the moving die plate and a plurality of tie rods extending through these bushes, it is difficult or impossible to bring the outer peripheral surface of each tie rod and the inner peripheral surface of each bush in uniform contact with each other, with the result that the moving die plate cannot move smoothly and parallelly. Moreover, it also is impossible to adjust the parallelism of the moving die plate.
With respect to this point, there is considered a countermeasure for increasing the accuracy of the work of assemblies to make the outer peripheral surface of each tie rod contact with the inner peripheral surface of each bush uniformly. When the accuracy of the work of assemblies increases, it is unavoidable that the tie rod is deformed due to the weight of the moving die plate, and the moving die plate is deformed due to external causes such as the influences of heat conveyed from the die or a pitch between the bushes is changed due to thermal expansion of the moving die plate. As a consequence, when the tie rods and the bushes are brought in contact with each other, they cannot contact with each other at their contact portions at all, or they are only brought in contact with each other at their contact portions in a line contact fashion, so that the moving die plate cannot move smoothly and parallelly.
Another countermeasure is a separate guide mechanism that can guide the moving die plate, for example. As this type of guide mechanism, there is known a guide mechanism that is generally referred to as a “linear motion guide” (often simply referred to as an “LM guide”). The related-art guide mechanism called a LM guide has the arrangement shown in FIGS. 1A and 1B.
As shown in FIGS. 1A and 1B, a related-art guide mechanism, generally denoted by reference numeral 1, includes a guide rail 3 fixed to an upper surface of a frame 2 and a slider 4 that engages with the guide rail 3 so as to slide along the guide rail 3. Two guide mechanisms 1 composed of the guide rail 3 and the slider 4 are prepared for a moving guide plate 5, and the two guide mechanisms 1 support the moving die plate 5 such that the moving die plate 5 can move close to or away from a fixed die plate 6.
The fixed die plate 6 is composed of a square plate-like member erected on the upper surface of the frame 2 and fixed to the frame 2 by a plurality of fixed screws 7a. The fixed die plate 6 has insertion holes 6a defined at its four corners, and tic rods 8, 9 are inserted into the insertion holes 6a, respectively. Screw portions 8a, 9a are formed at one end of the tie rods 8, 9, and fixed nuts 10 are screwed down on the respective screw portions 8a, 9a. The ends of the tie rods 8, 9 are brought in contact with a fixed plate 11 supported by a plurality of attachment screws 7b. 
The other ends of the four tie rods 8, 9 are elongated in the horizontal direction in parallel to each other, extended through bushes 5a of the moving die plate 5 and are fixed to the members of the frame 2 side. The moving die plate 5 is composed of a square plate-like member the size of which is approximately similar to that of the fixed die plate 6. The moving die plate 5 has the bushes 5a disposed at its four corners, and the tie rods 8, 9 are inserted into the bushes 5a with a predetermined clearance. The sliders 4 of the guide mechanisms 1 are downwardly attached to respective ends of the lower portion of the moving die plate 5, respectively.
The respective sliders 4 are fixed to the lower surface of the moving die plate 5 by a plurality of fixed screws 7c through an adjustment plate 12. The respective guide rails 3 are fixed to the upper surface of the frame 2 by a plurality of like fixed screws 7d. The guide rail 3 has a nearly gourd-like cross section in the width direction that crosses the longitudinal direction, and a guide groove 4a having a shape corresponding to the above gourd-like cross section is formed on the slider 4. The guide groove 4a and the guide rail 3 have a clearance of a predetermined spacing formed over approximately the whole peripheral surface thereof. This clearance has a large number of rolling elements interposed thereon, and these rolling elements can reduce frictional resistance generated between the guide rail 3 and the slider 4 to ensure that the slider 4 can move smoothly.
Since this guide mechanism 1, however, has no play to move except the direction in which it can move forwardly, the guide mechanism 1 can move smoothly in the forward direction, but it unavoidably increases frictional resistance in the directions other than the direction in which it proceeds. For this reason, even when the tie rods 8, 9 are brought in very slight contact with the bushes 5a as the moving die plate 5 is inclined a little, the guide mechanism 1 cannot move smoothly and moves clumsily. As a result, when the guide mechanism 1, such as the “LM guide”, is in use, it is unavoidable that the clearance between the tie rods 8, 9 and the bushes 5a should increase.
However, when clamping force is applied to the clamping apparatus using only the above-mentioned guide mechanism 1 under the condition in which an undesired substance, such as a foreign matter, is held in the die, the parallelism between the moving die plate 5 and the fixed die plate 6 is easily deteriorated. Since such deteriorated parallelism produces defective products, the deteriorated parallelism should be returned to the original normal state. In such case, it takes plenty of extra time, such as an adjustment time for adjusting the deteriorated parallelism and a time for dismounting the die from the moving die plate 5 and the fixed die plate 6 or mounting the die to the moving die plate 5 and the fixed die plate 6 one more time. There arises a problem that the operating ratio will be lowered.